The present invention relates to a vibration gyro that detects angular velocity.
A variety of vibration gyros, having tuning forks or tines of various shapes have been devised.
While mechanical type rotating gyros have been used as inertial navigation devices in aircraft and ships, the large size of these gyros made it difficult to use them in compact electronic equipment and transportation machinery.
In recent years, however, progress has been made in research in the development of practical compact vibration gyroscopes, in which a piezo-electric vibrating element is caused to vibrate an angular velocity current that is generated by the vibration caused by Coriolis force received because of the rotation of the vibrating element being detected by another piezo-electric element provided in the vibrating element, and such gyros are used car navigation systems and as detector for shaking in video cameras.
A vibration gyro of the past using a piezo-electric device is described below with reference to drawings. FIG. 29 is a perspective view showing a tuning fork type vibration gyro of the past.
This tuning fork type vibration gyro of the past is described below, with reference to FIG. 29. A resonator 71 made of a constant-resiliency metal such as Elinvar has a compound tuning fork structure. That is, the resonator 71 has joined onto the top part of the first beams 72 and 73 the second beams 74 and 75.
The piezo-electric element or the piezo-electric material driving section and drive electrode 76 are attached to the second beam 73.
While it is not shown in the drawing, in the same manner another similar driving section and drive electrode are attached to the first beam 72.
The piezo-electric element or the piezo-electric material driving section and drive electrode 77 are attached to the second beam 75.
While it is not shown in the drawing, in the same manner another similar driving section and drive electrode are attached to the first beam 74.
In this structure, the direction in which a beam extends is taken as the Z-axis direction.
The action of the above-noted structure will be described. As a result of an AC voltage that is applied to the drive electrode 76, the first beams 72 and 73 exhibit a first bending vibration which displaces them to the left and to the right. In the description which follows, this will be called xe2x80x9cintraplane vibration,xe2x80x9d since it is normally customary to consider the vibration of a tuning fork in a single plane to be the ideal case.
In response to this intraplane vibration, the second beams 74 and 75 that are joined to the first beams 72 and 73 exhibit intraplane vibration. If the overall tuning fork is caused to rotate about the Z axis at an angular velocity of xcfx89, a Coriolis force Fc acts in a direction that is perpendicular to the intraplane vibration.
This Coriolis force Fc can be expressed by the following relationship.
Fc=Mxc2x7xcfx89xc2x7V
In the above relationship, M is the mass of the first beams 72 and 73, or of the second beams 74 and 75, and V is the velocity of the vibration.
In accordance with the Coriolis force Fc, a second bending vibration is excited which has a displacement in directions that are perpendicular to the intraplane vibration.
This will be called hereinafter extraplanar vibration. By detecting the AC voltage that is generated by this extraplanar vibration using the detection electrode 77, it is possible to calculate and know the angular velocity xcfx89.
However, a vibration gyro of the past had the following problem. In general when supporting a vibrating element, to minimize the effect of the support on the vibration, support is made at a node at which the vibrating element does not move when vibrating.
In the case of the tuning fork having the configuration shown in FIG. 29, the intraplanar vibration node is at the furcated part, and while this part almost exhibits no movement, with extraplanar vibration excited by Coriolis force, there is no part that does not move due to vibration. Therefore, regardless of the location and method of support, there support will affect the vibrating element.
In general a tuning fork is supported near the center of the furcated part, and in contrast to intraplanar vibration of the vibrating element 71, which changes hardly at all whether supported at this location or not, with extraplanar vibration there is a change in the resonant frequency which can be as much as several percent.
Therefore, the resonant frequency for extraplanar vibration can change several percent, depending upon the method of support.
Extraplanar vibration is excited by Coriolis force with a frequency of the intraplanar vibration, the excitation efficiency being dependent upon the extraplanar vibration resonant frequency.
If there is distance between the intraplanar vibration resonant frequency and the extraplanar vibration resonant frequency, it is not possible cause sufficient excitation in the extraplanar vibration mode, and if there are large changes in the extraplanar vibration resonant frequency caused by a slight change in the support, the excitation efficiency will change greatly, making highly accurate detection impossible, this problem hindering a sufficient application of vibration gyros of the tuning fork type.
Because a vibration gyro detects a Coriolis force that acts in a direction that is perpendicular to the excitation direction, an element having a shape that is symmetrical about a center of a plane that is perpendicular to rotation direction to be detected is used, and at present a beam type is most commonly used.
However, such a beam-type element is difficult to support and difficult to support without affecting the vibrating element, and makes it impossible to completely prevent leakage of vibration to the outside. Easy-to-supports examples devised in the past include a four-beam tuning fork and a multiple beam tuning fork.
For example, there is the four-beam tuning fork vibration gyro disclosed in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083.
This four-beam tuning fork has a center symmetry within a plane that is perpendicular to the rotation direction to be detected, the same as with a single-beam type, and has a further feature of not vibrating at the bottom surface of its base part, thereby enabling complete isolation of the vibration with the outside.
In the four-beam tuning fork type vibration gyro disclosed in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083, of the 6 existing primary vibration modes of the four-beam tuning fork, vibration modes for which the drive and Coriolis force are perpendicular are selected, primary couplings between these modes being used to detect the Coriolis force, thereby achieving a vibration gyro that has almost no vibration at its base part.
The 6 primary vibration modes of a four-beam tuning fork having good symmetry are described below, with reference to the drawings.
FIG. 1 to FIG. 3 show front views of a general four-beam tuning fork, in which hatching is used to show the fixed condition of the bottom surface of the base part thereof.
The sizes of the various parts of this four-beam tuning fork are a total length of 4.8 mm, a base part length of 1.92 mm, a beam length of 2.88 mm, a base part width of 1.2 mm, a beam width of 0.48 mm and a groove width of 0.24 mm.
FIG. 17 through FIG. 22 are cross-section view showing this four-beam tuning fork as seen from the ends of the beams, the 6 primary vibration modes that each of these beams of the four-beam tuning fork has, the sequence of the drawings being that of increasing frequency as calculated using finite element analysis and verified later by experiment. The last torsional mode was not verifiable by experiment, however.
FIG. 23 through FIG. 28 show cross-section views of the beams of the four-beam tuning fork as seen from the ends of the beams, in the same manner, with the overall width of the tuning fork reduced by 1% but the thickness remaining the same.
In contrast to FIG. 17 through FIG. 22, the cross-sections of the beams are rectangular, the sequence of the drawings in this case as well being that of increasing frequency as calculated using finite element analysis and verified later by experiment. The last torsional mode was not verifiable by experiment, however, in this case as well.
First, the vibration modes for the case in which the cross-sections of the beams are square will be described, using FIG. 17 through FIG. 22.
In FIG. 17, the arrows indicate the swing direction of the beam at some instant, the mode having these swing directions being referred to as mode 1, the centers of the four beams swinging so as to describe a non-square rectangle, the characteristic vibration frequency being 38.730 kHz.
In FIG. 18, the arrows in the drawing indicate the swing directions of the beams at some given instant in time, and the vibration mode with these swing directions will be called vibration mode 2, the centers of the four beams swinging so as to maintain a square shape, the characteristic vibration frequency being 38.841 kHz.
In FIG. 19, the arrows in the drawing indicate the swing of the four beams at some instant in time, this vibration mode being called vibration mode 3, in which the centers of the four beams swing so as to form a diamond shape, the characteristic vibration frequency being 39.160 kHz.
In FIG. 20, the arrows indicate the swing of the four beams at some instant in time, this vibration mode being called vibration mode 4, in which the centers of the four beams swing in mutually parallel directions, the characteristic vibration frequency of which is 39.483 kHz.
In FIG. 21, the arrows indicate the swing of the four beams at some instant in time, this vibration mode being called vibration mode 5, in which the centers of the four beams swing in mutually parallel directions, the characteristic vibration frequency of which is 39.483 kHz.
In FIG. 22, the arrows indicate the swing of the four beams at some instant in time, this vibration mode being called vibration mode 6, in which the centers of the four beams swing so as to be twisted, the characteristic vibration frequency being 40.150 kHz. The reason mode 6 could not be verified by experiment was the extreme vibration of the semi-fixed base part.
Next, the vibration modes for the case in which the cross-sections of the beams are rectangular will be described, using FIG. 23 through FIG. 28.
In FIG. 23, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 1, in which the centers of the four beams swing in mutually parallel directions, the characteristic vibration frequency being 36.617 kHz.
In FIG. 24, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 2, in which the centers of the four beams swing in directions that are mutually parallel, the characteristic vibration frequency being 36.939 kHz.
In FIG. 25, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 3, in which the centers of the four beams swing so as to form a diamond shape, the characteristic vibration frequency being 37.099 kHz.
In FIG. 26, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 4, in which the centers of the four beams swing in mutually parallel directions, the characteristic vibration frequency being 37.266 kHz.
In FIG. 27, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 5, in which the centers of the four beams swing in mutually parallel directions, the characteristic vibration frequency being 37.608 kHz.
In FIG. 28, the arrows indicate the swing of the beams at some instant in time, this vibration mode being called mode 6, in which the centers of the four beams swing so that the four-beam tuning fork is twisted, the characteristic vibration frequency being 38.101 kHz.
In this case as well, the reason that mode 6 could not be verified by experiment was the extreme vibration of the semi-fixed base part.
By way of description of the action of the above-noted configuration, in the case of the four-beam tuning fork vibration gyro disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 6-258083, of the six primary vibration modes of the four-beam tuning fork based on the vibration modes for the case of a rectangular shape, vibration modes for driving and detection vibration modes for which the Coriolis force is perpendicular to the driving modes are selected, the configuration being made such as to support these driving and detection modes.
In the first embodiment, the vibration mode 4 for a rectangular shape that is shown in FIG. 26 is taken as the driving vibration mode, and the vibration mode 5 for a rectangular shape that is shown in FIG. 27 is taken as the detection vibration mode. (Although it is not clearly indicated, it is not usual to select a mode with the lower characteristic vibration frequency as the detection vibration mode.)
In the second embodiment, the vibration mode 3 for a rectangular shape that is shown in FIG. 25 is taken as the driving vibration mode, and the vibration mode 1 for a square shape that is shown in FIG. 17, and which does not exist in the case of the rectangular shape, is taken as the detection vibration mode, and a configuration for implementing this driving and detection is indicated.
In the third embodiment, a method is indicated for detecting the vibration mode 1 for a rectangular shape that is shown in FIG. 23 and the vibration mode 2 for a rectangular shape that is shown in FIG. 24, which are caused from the first-order coupling of the vibration mode 3 for a rectangular shape as shown in FIG. 25 and the vibration mode 1 for square shape excited by the Coriolis force shown in FIG. 17, and a configuration for implementing this driving and detection is indicated.
However, the following problems exist with the four-beam tuning fork that is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 6-258083. First, in the first embodiment, with the vibration mode 4 for a rectangular shape that is shown in FIG. 26 and the vibration mode 5 for a rectangular shape that is shown in FIG. 27, because of the difference between the characteristic vibration frequencies, it is not possible to achieve a large detection sensitivity due to the lack of sufficient excitation of vibration mode 5 by vibration mode 4.
With regard to this point, while the Japanese Unexamined Patent Publication (KOKAI) No. 6-258083 has language to the effect of using symmetry, that is, of using a square shape, in actuality there is no vibration mode such as vibration mode 4 and vibration mode 5 for a rectangular shape that are shown in FIG. 26 and FIG. 27 for the case of a square, and the vibration mode such as vibration mode 4 and vibration mode 5 appear for a square, as shown in FIG. 20 and FIG. 21.
Experimentally, if the difference in the characteristic vibration frequency for the two directions approaches approximately 100,000 ppm, coupling already cause the rectangular vibration mode 4 and vibration mode 5 shown in FIG. 26 and FIG. 27 to cease to exist.
Therefore, the first embodiment which is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 6-258083 is either implemented using a non-resonant four-beam tuning fork in which the frequency difference is greater than 100,000 ppm or by a resonant type which, even without Coriolis force, detects Coriolis force with an extremely high output being generated.
In the case of a non-resonant type, because the Coriolis force detection sensitivity will be poor, this will result in a worsened S/N ratio for Coriolis force detection, and in the case of a resonant type it is necessary to detect a Coriolis force from an output that is much larger than the output that is caused by the Coriolis force, this forcing the measurement to be performed with an extremely wide dynamic range, which is disadvantageous from the standpoint of achieving a high S/N ratio. Additionally, while there is a proposal of a mechanism to limit the output by using a closed loop, this does not change the S/N ratio.
Turning next to the remaining embodiments that are disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 6-253083, the rectangular vibration mode 5 shown in FIG. 25 is used for driving, and the rectangular vibration mode 1 or mode 2 shown in FIG. 23 and FIG. 24, respectively, or the square vibration mode 1 which is shown in FIG. 17 and which is generated from the coupling therebetween is used for detection.
In the case of a rectangular shape, if the vibration mode 6, for which detection is not possible, shown in FIG. 28, is eliminated, the vibration mode 3 which is shown in FIG. 25 is the only mode which coincides with the square.
There is a clear difference in characteristic vibration frequency between this and the vibration mode for detection.
With regard to this frequency difference, if one considers the vibration modes which are intrinsically different, even if it is possible to perform adjustment so that the characteristic vibration frequencies coincide, this would affect the overall symmetry of the tuning fork, thereby increasing the vibration noise, making it impossible to achieve a high Coriolis force detection S/N ratio.
Accordingly, it is an object of the present invention to provide a vibration gyro which solves the above-noted problems, this vibration gyro having good detection sensitivity and good detection accuracy.
To solve the foregoing object, a vibration gyro according to the present invention basically employs the technical structure that is described below.
Namely, a vibration gyro according to the present invention is made of a resilient material, comprising four beams and a base part that is integrally formed with the beams, wherein the four beams are disposed at equal distances and at uniform angular spacing with respect to the center part of the base part; a first part of the beams comprising at least a part of the beams selected from the beams, which are caused to make self-excitation resulting in a first vibration along a first direction that is not within a plane that includes the center lines of the selected two mutually adjacent beams and the first vibration being separable into a first bending vibration and a second bending vibration; a second part of the beams comprising at least a part of the beams selected from the beams and including at least one beam belonging to the first part of the beams, which are caused to make self-excitation resulting in a second vibration along a second direction different from the first direction and which is not within a plane that includes the center lines of the selected two mutually adjacent beams and the second vibration being separable into a first bending vibration and a second bending vibration; at least one electrode selected from a group of a drive electrode and a detection electrode each being made of piezo-electric element is provided on a side surface of each of the beams; and a voltage that is generated by bending vibration on at least a part of the beams is measured.
It is preferred that the vibration gyro according to the present invention be structured so that a piezo-electric drive electrode and a piezoelectric detection electrode are provided on all side surfaces of the beams, and a voltage generated by bending vibration from all the beams is measured.
Further, the vibration gyro according to the present invention may be structured so that the second vibration is caused by Coriolis force caused by rotation of the vibration gyro.
Because the vibration gyro according to the present invention employs the above-described structure, by arranging the four beams in a quad-divided square having good symmetry, the base part is substantially stationary for either employed vibration, without using vibration that is affected at the support part, such as by extraplanar vibration in the tuning fork type, and an angle can be detected with good accuracy without performance being affected by the method of support. Matching of the excitation to obtain a large output signal and the resonant frequency for detection can be achieved without placing great expectations on machining and assembly precision, and because a large output signal in the resonant detection direction is obtained with the structure, and a structure which can cancel output other than Coriolis force is obtained, and so noise is small and a high S/N can be achieved.
Additionally, because the beams for acceleration and detection are separate, DC drift due to phase shifting caused by vibration is substantially nil.
FIG. 1 is a perspective view that shows an outer view of a fourbeam tuning fork vibration gyro according to the present invention.
FIG. 2 is a perspective view that shows the locations of electrodes of four-beam tuning fork vibration gyro according to the present invention.
FIG. 3 is a drawing which shows a cross-section view of electrode structure in the Y-axis direction of a vibration gyro which is a first embodiment according to the present invention as viewed from the ends and a schematic wiring diagram thereof.
FIG. 4 is a drawing which shows a cross-section view of electrode structure in the Y-axis direction of a vibration gyro which is a second embodiment according to the present invention as viewed from the ends and a schematic wiring diagram thereof.
FIG. 5 is a drawing which shows a cross-section view of electrode structure in the Y-axis direction of a vibration gyro which is a second embodiment according to the present invention as viewed from the ends and a schematic wiring diagram thereof.
FIG. 6 is a drawing that shows an outer view of a vibration element enclosed in a cylindrical tube of a four-beam tuning fork vibration gyro which is a mode of embodiment of the present invention.
FIG. 7 is a drawing which illustrates the operation of a four-beam tuning fork vibrating gyro that is an embodiment of the present invention, and which schematically shows the cross-sections of the beams in the Y-axis direction as seen from the ends thereof.
FIG. 8 is a drawing which illustrates the operation of a four-beam tuning fork vibrating gyro that is an embodiment of the present invention, and which schematically shows the cross-sections of the beams in the Y-axis direction as seen from the ends thereof.
FIG. 9 is a drawing which illustrates the operation of a four-beam tuning fork vibrating gyro that is an embodiment of the present invention, and which schematically shows the cross-sections of the beams in the Y-axis direction as seen from the ends thereof.
FIG. 10 is a drawing which illustrates the operation of a four-beam tuning fork vibrating gyro that is an embodiment of the present invention, and which schematically shows the cross-sections of the beams in the Y-axis direction as seen from the ends thereof.
FIG. 11 is a perspective view that shows a piezo-electric element used in a vibration gyro of four-beam tuning fork type which is an embodiment of the present invention.
FIG. 12 is a perspective view that shows a piezo-electric element used in a vibration gyro of four-beam tuning fork type which is an embodiment of the present invention.
FIG. 13 is a front view that shows an ordinary four-beam tuning fork.
FIG. 14 is a waveform diagram that shows signals from piezo-electric elements.
FIG. 15 is a waveform diagram that shows signals from piezo-electric elements.
FIG. 16 is a drawing which illustrates the operation in the form of vector representations of signals from piezo-electric elements.
FIG. 17 through FIG. 28 are drawings which illustrate the operation of an ordinary four-beam tuning fork vibrating gyro, and which schematically show the cross-sections of the beams as seen from the ends thereof.
FIG. 29 is a perspective view that shows a tuning fork vibration gyro according to the prior art.
FIG. 30 is a voltage waveform diagram that shows the effect of Coriolis force a vibration gyro.
FIG. 31 is a voltage waveform diagram that shows the effect of Coriolis force in a vibration gyro.
FIG. 32 is a voltage waveform diagram that shows the effect of Coriolis force in a vibration gyro.
FIG. 33 is a voltage waveform diagram that shows the effect of Coriolis force in a vibration gyro.
FIG. 34 is a drawing which shows the cross-sections of the beams of a four-beam tuning fork vibrating gyro that is a fourth embodiment of the present invention as viewed from the ends of the beams and a circuit block diagram thereof, and a schematic wiring diagram thereof.
FIG. 35 is a drawing which shows the cross-sections of the beams of a four-beam tuning fork vibrating gyro that is a fifth embodiment of the present invention as viewed from the ends of the beams and a circuit block diagram thereof, and, a schematic wiring diagram thereof.
FIG. 36 is a drawing which shows the cross-sections of the beams of a four-beam tuning fork vibrating gyro that is a sixth embodiment of the present invention as viewed from the ends of the beams and a circuit block diagram thereof, and a schematic wiring diagram thereof.
FIG. 37 is a drawing which shows the cross-sections of the beams of a four-beam tuning fork vibrating gyro that is a seventh embodiment of the present invention as viewed from the ends of the beams and a circuit block diagram thereof, and a schematic wiring diagram thereof.
FIG. 38 is a drawing which shows the cross-sections of the beams of a four-beam tuning fork vibrating gyro that is the seventh embodiment shown in FIG. 37 as viewed from the ends of the beams and a detailed circuit example thereof.
FIG. 39 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.
FIG. 40 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.
FIG. 41 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.
FIG. 42 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.
FIG. 43 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.
FIG. 44 is a drawing which illustrates the operation in the form of cross-sectional representations of beams as viewed from the ends of beams of a four-beam tuning fork vibration gyro according to the present invention.